This project examines nervous system diseases associated with human herpes virus infections. Agents include neurotropic herpes simplex virus types l and 2 (HSV~1, ~2) and varicella zoster virus (VZV), as well as four human herpesviruses known or suspected to infect the nervous system (cytomegalovirus [CMV], Epstein~Barr virus [EBV], and human herpesvirus types 6 and 7 [HHV~6, ~7]). Experimental models are used to examine mechanisms underlying production of neural lesions. Problems of particular interest are: the role of infection with HSV, VZV and other herpesviruses in the production of CNS and PNS disease, including (i) acute encephalitis, (ii) infections during nervous system development, (iii) chronic demyelination, and (iv) mechanisms of CNS arteritis and stroke induced by neurotropic herpesviruses. During FY 1993 an in situ polymerase chain reaction (ISPCR) method was developed to localize HSV~2 DNA sequences in tissue sections in acute and latent stages of infection in mice. With appropriate controls, it was shown that in acute infection, cell labeling in brain was similarly distributed to viral antigen in adjacent sections, while in latent infection, ISPCR labeled some cells not detected by any other method. In trigeminal ganglia, more neurons were labeled by ISPCR than by in situ hybridization during latent infection. The enhanced sensitivity of ISPCR over previous methods makes it possible to more completely define sites of HSV latency and persistence in neural tissues than previously possible. A study to detect HSV DNA sequences in human neonatal autopsy tissues by PCR was completed. This technique is more sensitive than previous methods to detect HSV infection in the neonatal nervous system. It provides a basis for ISPCR tests to localize HSV DNA in human brains. To develop new measures of vaccine efficacy in preventing neurotropic virus spread along neural pathways, mice were immunized with a recombinant vaccinia virus expressing control or HSV~1 glycoprotein D genes. The HSV recombinant elicits a high level of neutralizing antibody, protects from lethal HSV~1 intranasal challenge and reduces virus titers in neural tissues. While virus spreads to the CNS along olfactory, somatosensory, sympathetic and parasympathetic pathways in non~immunes, CNS spread in immunes is restricted to a few glial cells in trigeminal pathways and is associated with an intense lymphocytic response. Critical evaluation of vaccine efficacy for neurotropic viruses will require inclusion of histological endpoints.